http.HandlerFunc wrapper technique

handler.go

//https://medium.com/@matryer/the-http-handler-wrapper-technique-in-golang-updated-bc7fbcffa702

//wraps the handler do do things before and/or after
func auth(h http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		fmt.Println("Before")
		h.ServeHTTP(w, r)
		fmt.Println("After")
	})
}

//Checks for valid request otherwise retunr a error
func checkAPIKey(h http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if len(r.URL.Query().Get("key")) == 0 {
			http.Error(w, "missing key", http.StatusNotFound)
			return
		}
		h.ServeHTTP(w, r)
	})
}

//Refering helps us to run even if the handler panics
func log(h http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		fmt.Println("before")
		defer fmt.Println("after")
		h.ServeHTTP(w, r)
	})
}

// To check a required paramentrs
func mustParams(h http.Handler, params ...string) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {

		q := r.URL.Query()
		for _, param := range params {
			if len(q.Get(param)) == 0 {
				http.Error(w, "missing "+param, http.StatusBadRequest)
				return // exit early
			}
		}
		h.ServeHTTP(w, r) // all params present, proceed
	})
}

/*
http.Handler("/user", MustParams(handleUser, "key", "auth"))
http.Handler("/group", MustParams(handleGroup, "key"))
http.Handler("/items", MustParams(handleSearch, "key", "q"))
*/

//check if the auth parameter is present
func mustAuth(h http.Handler) http.Handler {
	checkauth := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		err := validateAuth(r.URL.Query().Get("auth"))
		if err != nil {
			http.Error(w, "bad auth param", http.StatusUnauthorized)
		}
		h.ServeHTTP(w, r)
	})
	return mustParams(checkauth, "auth")
}

func validateAuth(arg string) error {
	return nil
}